A lot of academic and commercial information is invisible to general search engines such as Google, as this article explains.
Lewandowski, Dirk and Philipp Mayr. 2006. Exploring the academic invisible web.Library Hi Tech, [online] 24(4), 529. Available: ABI/INFORM Global. [accessed 13 July 2010]
Why not take a couple of minutes to look at Google v. Library Databases and see what you think.